the vast majority of things you "see" out of the corner of your eye are, what "in the trade" are called floaters, or in other words coagulation of vitreous humour. That said whilst I don't believe most of it, I keep an open mind.
You can see 'floaters' across the centre of your eyes as well as in the corner Ed. As you say, they are little 'bubbles', for want of a better word, that float in the eye fluid. At one time I was seeing quite a lot of them and the optician explained they were nothing to be overly concerned about.
